1. Field of the Invention
This invention relates to recess-protrusion structure body comprising a base plate and at least one protruding region, which has been formed on the base plate. This invention also relates to a process for producing the recess-protrusion structure body. This invention further relates to a piezoelectric device comprising a piezoelectric film, which contains at least one protruding region, and electrodes for applying an electric field across the piezoelectric film, the piezoelectric film and the electrodes being formed on a base plate. This invention still further relates to an ink jet type recording head, which is provided with the piezoelectric device, and an ink jet type recording apparatus, which is provided with the ink jet type recording head.
2. Description of the Related Art
Piezoelectric devices provided with a piezoelectric film, which has piezoelectric characteristics such that the piezoelectric film expands and contracts in accordance with an increase and a decrease in electric field applied across the piezoelectric film, and electrodes for applying the electric field in a predetermined direction across the piezoelectric film have heretofore been used as actuators to be loaded on ink jet type recording heads, and the like. As piezoelectric materials, there have heretofore been known composite oxides having a perovskite structure, such as lead zirconate titanate (PZT).
As described in, for example, Japanese Unexamined Patent Publication No. 2005-153353, it has been reported that the piezoelectric film is not constituted of a continuous film and is constituted of a pattern composed of a plurality of protruding regions, which are separated from one another, such that the expansion and contraction of each of the protruding regions may occur smoothly and such that a large displacement quantity may be obtained. In order for a desired strain displacement quantity to be obtained, the piezoelectric film is formed so as to have a thickness falling within the range of approximately 1 μm to approximately 5 μm. The thickness of the piezoelectric film falling within the aforesaid range is larger than the thickness of each of the electrodes, and the like, on the order of nanometers (e.g., the thickness of 200 nm). As described in, for example, International Patent Publication No. WO01/082344, heretofore, the piezoelectric films, such as the PZT films, are ordinarily subjected to the patterning with dry etching processing.
Ordinarily, the dry etching processing is known as anisotropic etching processing. However, PZT, or the like, is a material which is hard to etch. Also, the piezoelectric films are thicker than the electrodes, and the like, having a thickness on the order of nanometers. Therefore, the drying etching processing of the piezoelectric films is harder to perform than the processing of the electrodes, and the like. Accordingly, in cases where the dry etching processing is performed on the piezoelectric films, perfectly anisotropic etching is not always capable of being achieved. FIG. 6 is an explanatory sectional view showing problems encountered with the conventional technique. Specifically, as illustrated in FIG. 6, side faces 71a, 71a, . . . of a protruding region 71 having been formed with the dry etching processing are apt to have taper shapes. In FIG. 6, reference numeral 70 represents a base plate.
In the cases of the ink jet type recording heads, such that enhanced image quality of recorded images may be obtained, a high level of uniformity in piezoelectric characteristics of the plurality of the protruding regions constituting the piezoelectric films is required of the ink jet type recording heads. However, with the dry etching processing, which yields the protruding regions having the taper side face shapes, it is not always possible to accomplish accurate matching of angles of the side faces of the plurality of the protruding regions. Hereafter, there will be the possibility that the adverse effects of a variation in piezoelectric characteristics, which variation occurs due to a variation in shapes of the protruding regions, upon the image quality of the recorded images will not be capable of being ignored. In cases where the accuracy of the side face shapes of the protruding regions is taken into consideration, there should preferably be employed a patterning technique, such that the side face shapes of the protruding regions are capable of being reliably set at shapes approximately normal to a surface of a base plate, on which the protruding regions are formed.
Also, with the piezoelectric films, such as the PZT films, the problems are encountered in that, since the dry etching processing is hard to perform due to the material characteristics and the thicknesses of the piezoelectric films, a long time is required to perform the patterning. Further, with the dry etching processing, since a vacuum process is necessary, the cost is not capable of being kept low.
As a patterning technique for electrodes, dielectric substances, and the like, a lift-off technique has heretofore been known. (The lift-off technique is described in, for example, Japanese Unexamined Patent Publication No. 53(1978)-070764, U.S. Pat. No. 6,156,672, and U.S. Patent Application Publication No. 20040248047.) The lift-off technique will be described hereinbelow with the patterning of electrodes being taken as an example.
FIGS. 7A, 7B, and 7C are explanatory sectional views showing problems encountered with a conventional technique. FIG. 7D is a plan view of FIG. 7C. With the lift-off technique, as illustrated in FIG. 7A, a resist layer (or a sacrifice layer) 72, which is capable of being removed selectively, is formed in a predetermined pattern in electrode non-forming regions on a base plate 70. Thereafter, as illustrated in FIG. 7B, a solid electrode film 73X is formed on the base plate 70. Thereafter, as illustrated in FIG. 7C, processing for removing the resist layer 72 is performed. With the processing, the areas of the solid electrode film 73X, which areas are located on the resist layer 72, are removed together with the resist layer 72. In this manner, an electrode 73 is capable of being formed in a predetermined pattern.
In the cases of the patterning of a thin film for the formation of an electrode, or the like, which has a thickness on the order of nanometers, the patterning is capable of being performed accurately with the lift-off technique, and the side face of the protruding region, which is formed with the patterning, is capable of being set at a shape approximately normal to the base plate surface.
However, in cases where the lift-off technique is applied directly to the patterning of a piezoelectric film, which has a large thickness on the order of microns, since the thickness of the piezoelectric film located on the resist layer (or the sacrifice layer) is large, it is not always possible to remove the resist layer (or the sacrifice layer) and the unnecessary regions of the piezoelectric film, which regions are located on the resist layer (or the sacrifice layer). Also, in such cases, it is necessary that the unnecessary regions of the piezoelectric film and a necessary region of the piezoelectric film are separated from each other, and that the unnecessary regions of the piezoelectric film are thus removed. Therefore, as illustrated in FIGS. 7C and 7D, the smoothness of shapes of side faces 73a, 73a, . . . of the protruding region is apt to become bad, and pattern loss often occurs. Thus it is not always possible to obtain a pattern with a good shape accuracy.
Recently, with respect to organic materials, a technique for patterning protruding regions, which has a shape approximately normal to a base plate surface, with a high definition by use of a nano-imprinting technique has been used in practice. However, the nano-imprinting technique is not capable of being applied to inorganic materials.